NMSU Graduate Student Researches Cutthroat Trout Decline

LAS CRUCES - A popular sportfish might spell bad news for New Mexico’s state fish. The brown trout, which are not native to North America, are a threat to the New Mexico-native Rio Grande cutthroat trout.

Brown trout are the most widespread invasive trout species in New Mexico, and can tolerate a broader range of water temperatures than cutthroat trout. They are also larger and more aggressive than cutthroat trout. Lauren Flynn, New Mexico State University graduate student in the College of Agricultural, Consumer and Environmental Sciences’ Department of Fish, Wildlife and Conservation Ecology, is conducting research to find what can be done to conserve Rio Grande cutthroat trout populations.

“I predict that warm stream temperatures and brown trout will negatively impact Rio Grande cutthroat trout. Even though warm temperatures should help the cutthroat trout grow, I think brown trout are outcompeting the cutthroat for food in warmer streams,” she said.

She is collaborating with the U.S. Geological Survey Research Unit Leader and NMSU Affiliate Professor Colleen Caldwell and post-doctoral researcher Brock Huntsman on this research project.

This is Flynn’s second year working on this project. She and her advisers go to the Santa Fe National Forest and Carson National Forest to do their research. They start with a long drive up to Northern New Mexico, which is Flynn’s least favorite part of the research trips.

“On any given field trip to do our work, we’ll drive over a thousand miles. I like doing the field work, not so much the driving,” she said. Once they arrive, they set up camp, sometimes right next to a stream, and other times a short hike away from the stream. After cooking dinner on a stove brought from home, the team will set up their tents and prepare for the long day ahead. Early in the morning, their day begins.

“It’s about an eight- to 10-hour day. It’s a lot of fun, but a lot of work,” Flynn said.

They begin with setting up nets to block off 300 meters of stream, which are the same 300 meters they return to every season. Before capturing the fish, the researchers sample aquatic bugs to see what food is available for the trout. Now, the fun part begins; time to study the fish.

The best way to catch fish without killing them is to use electricity. The team uses a backpack electrofisher, which weighs about 25 pounds, to stun the fish and cause them to contract their muscles and disable them from swimming away. The fish are scooped up from the water with a net and the team examines them.First, they check to see if they have previously captured that fish by scanning it for a tag. This tag is an electronic microchip that uniquely identifies the fish and looks like a tiny vitamin capsule made of glass. If the fish does not have a tag, they will inject one into the muscle below the fish’s dorsal fin. Once they identify or tag the fish, they measure its length, weight and diet. After making all their observations and measurements, they release the fish back into the stream.

All of this hard work is done with the hope of helping to preserve New Mexico’s Rio Grande cutthroat trout populations.

“Depending on what we find, the results of this project could help managers pinpoint Rio Grande cutthroat trout populations that are most threatened by brown trout. We are hoping temperature is useful criteria,” Flynn said.

An easier solution to this problem would be to just eradicate brown trout, but Flynn said it is not the best idea for many reasons. Some of those reasons are that it would make sport fishers unhappy and it would cost a lot of money. Instead, data-driven research can help prioritize and focus management of the native cutthroat trout. Flynn anticipates a compromise, which will conserve the native cutthroat trout without completely eradicating the invasive, but popular, brown trout.